Wallboard or gypsum board is well-known. Generally, gypsum board is formed by first preparing the gypsum paper in paper making machines. Typically, the gypsum paper is manufactured by driving the plies through a sizing bath which may contain alum and/or rosin for sizing the gypsum paper; whereupon the gypsum paper is then formed to the desired thickness and collected off the end of the machine. Gypsum board is then prepared from the sheets of gypsum paper by putting a gypsum mixture between the sheets of gypsum paper to form a composite sandwich of gypsum paper and gypsum mixture. The composite board is then semi-dried and cut to the desired lengths. The cut lengths of the board are then put into a high temperature kiln to complete the drying of the gypsum board.
Water-repellent wallboard or gypsum board can be prepared by several methods. The most common method practiced in the industry is the blending of an asphalt emulsion into the wallboard paste or mixture. While this method produces a wallboard having good water repellency, it has the distinct disadvantage of needing to maintain the asphalt emulsion in a molten state during processing. Due to this requirement, wallboard plants must plan well in advance if they wish to make a batch of water-repellent wallboard.
It is also known in the art that silicone hydride fluids can be added to gypsum to make water-repellent mixtures for use in preparing water-repellent building materials. Roth et al., U.S. Pat. No. 4,835,014, disclose a method for imparting water repellency to an absorbent inorganic building material which comprises contacting at least a portion of the surface of the building material which is to be rendered water-repellent with at least partially liquid water having a temperature of from 0.degree. to about 150.degree. C. and thereafter applying a solution containing an organosilicone compound which imparts water repellency to an inorganic building material and a water-immiscible solvent to the wet surface.
Steinbach et al., U.S. Pat. No. 4,643,771, disclose a process for the production of a water-repellent porous plaster molding consisting essentially of producing a foam from water, an organosulfonate or organosulfate foaming agent and polymethyl-hydrogen-siloxane, adding this foam to a paste of plaster powder in water, and letting the mixture set, the surfactant and the siloxane each being present in 0.1 to 0.5 part by weight per 100 parts by weight of the plaster.
Traver et al., U.S. Pat. No. 4,258,102, disclose treating gypsum paper with a mixture of a silanol organopolysiloxane polymer where the polymer has a viscosity varying from 1,000 to 1,000,000 centipoise at 25.degree. C. and in which there is mixed a liquid suspension of colloidal silica.
However, it has been found that when the silicone fluids of the prior art are employed in preparing water-repellent froths for use in rendering wallboard water-repellent, there is a significant increase in the froth density, i.e., defoaming, which detrimentally affects the weight to strength ratio of the finished wallboard product. Attempts to solve this problem have included the use of additional amounts of soap. However, while this succeeded in decreasing the froth density, it also concurrently resulted in a reduction in water repellency.
It would therefore represent a notable advance in the state of the art if a silicone fluid could be provided which provided for improved water repellency and which does not detrimentally effect the strength of the finished wallboard product.